In the helicopter rotor art, helicopters are generally divided into broad categories, namely, articulated rotor, flex-rotor and rigid rotor. In an articulated rotor, the helicopter blades are connected to the helicopter hub through a blade-to-hub connection so as to be supported from the helicopter rotor hub for rotation therewith, and so as to be moveable in pitch change (torsional), lead-lag (horizontal), and flapping (vertical) motion with respect to the hub, and to have the loads generated during the creations of these motions reacted from the helicopter blade through the blade-to-hub connection back to the hub. Centrifugal loads generated by the blades during rotation must similarly be reacted back to the hub. In articulated rotors, the blade is mounted and supported from the hub so as to be pivotable about fixed pitch change, lead-lag and flapping axes.
A flex-rotor is to be distinguished from an articulated rotor in that these motions and loads are established and accommodated by the flexibility of the parts involved.
In the early articulated rotor art, each blade was connected to the rotor through plain bearings, one of which was mounted for rotation about each of the lead-lag, pitch change and flapping axes. This construction was heavy, required lubrication, substantial maintenance and is expensive to manufacture and is not ballistically tolerant. Such a construction is shown in U.S. Pat. No. 2,853,141 to Leoni.
A substantial advancement in the art took place when Rybicki taught in U.S. Pat. No. 3,759,632 the substitution of elastomeric bearings for the plain bearings of the prior art. While we have retained the through bearing load path configuration of Rybicki, our invention advances the art by replacing the metallic spindle with a pin wrapped advanced composite strap which maintains prior characteristics of low drag and strength, but adds the inherent advanced features of composite materials.
Our invention incorporates modern composite materials into the yoke or spindle of a helicopter rotor and uses them in combination with a spherical elastomeric bearing to produce an articulated helicopter rotor in which the blades are capable of lead-lag, flapping and pitch change motion about coincident axes, and wherein the connection between the blades and the hub is capable of accommodating these motions and reacting these loads, while simultaneously reacting the centrifugal load generated by the blades during rotor rotation.
Use of high strength fibers in composite strap members is not new in the helicopter art, however, none of the prior art teaches the combination of a spherical elastomeric bearing connected in series to a continuously wrapped composite belt made of bonded high strength fibers pin wrap connected to the hub and blade, and passing through the central aperture of the elastomeric bearing to produce a composite yoke, which bearing and yoke coact to accommodate all of the pitch change, lead-lag and flapping motions and to react all pitch change, lead-lag, flapping and centrifugal loads between the helicopter blade and hub. For example, Barbier et al U.S. Pat. No. 4,892,462, granted Jan. 9, 1990, teaches the use of such bonded fibers pin-wrapped to the hub in a flex-rotor construction, but does not utilize that construction in combination with the spherical elastomeric bearing to obtain the advantages gained herein. DeRosa U.S. Pat. No. 4,419,051, granted Dec. 6, 1983, teaches an articulated helicopter rotor utilizing two bearings and a composite strap but with the composite strap positioned outboard of both bearings to thereby increase the frontal area and hence drag of the rotor. Reyes U.S. Pat. No. 4,227,857, granted Oct. 14, 1980, teaches a helicopter flex-rotor with no lead-lag or flapping bearings and a composite loop positioned outboard of the general rotor construction to similarly increase the frontal area and hence drag thereof. Mautz U.S. Pat. No. 3,578,877, granted May 18, 1971, teaches what appears to be a rigid rotor utilizing a composite straps pin connecting diametrically opposed blades to react blade centrifugal loads. Mouille et al U.S. Pat. No. 4,273,511, granted Jun. 16, 1981, teaches composite fibers pin wrapped to the hub and then extending through the entire blade for bonding thereto. McArdle U.S. Pat. No. 4,242,048, granted Dec. 30, 1980, teaches what is apparently a flex-rotor construction without articulating hinges in which criss-crossed flex-straps pin connects the blade to the hub. Lovera et al U.S. Pat. No. 4,369,019, granted Jan. 18, 1983, teaches a U-shaped yoke, presumably made of metal, to connect the helicopter blade to the hub and does not use pin-wrap construction. Such yokes fabricated of composite material are known to be old in Hibyan et al U.S. Pat. Nos. 4,585,393 and 4,568,246, granted on Apr. 29, 1986 and Feb. 4, 1986, respectively.